The Malthusian trap, named after political economist Thomas Robert Malthus, suggests that for most of human history, income was largely stagnant because technological advances and discoveries only resulted in more people, rather than improvements in the standard of living. It is only with the onset of the agricultural revolution in Britain and Holland and the Industrial Revolution in the 18th century that the income per person began to dramatically increase in some countries, and they broke out of the trap; it has been shown, however, that the escape from the Malthusian trap can also generate serious political upheavals. It is argued that many countries in tropical Africa still find themselves in the Malthusian trap.
Malthus' theoretical argument
It was Thomas Malthus who first made the argument that in "every age and in every state" population increases are limited by the means of subsistence, and that when the means of subsistence increases, population will also increase, and that the population increase will be limited by "misery and vice". This pessimistic view on the impossibility of real progress was first made in 1798, ironically, just as the Industrial Revolution was getting underway; however, it took several decades for the industrialization to raise the living standards of lower income people in countries where it occurred.
In accordance with the theory, cross-country evidence indicates that technological superiority and higher land productivity had significant positive effects on population density but insignificant effects on the standard of living, during the time period 1–1500 AD. In addition, scholars have reported on the lack of a significant trend of wages in various places over the world for very long stretches of time. In Babylonia during the period 1800 to 1600 BC, for example, the daily wage for a common laborer was enough to buy about 15 pounds of wheat. In Classical Athens in about 328 BC, the corresponding wage could buy about 24 pounds of wheat. In England in 1800 AD the wage was about 13 pounds of wheat.:50 In spite of the technological developments across these societies, the daily wage hardly varied. In Britain between 1200 and 1800, only relatively minor fluctuations from the mean (less than a factor of two) in real wages occurred. Following depopulation by the Black Death and other epidemics, real income in Britain peaked around 1450-1500 and began declining until the British Agricultural Revolution.
Robert Fogel published a study of lifespans and nutrition from about a century before Malthus to the 19th century that examined European birth and death records, military and other records of height and weight that found significant stunted height and low body weight indicative of chronic hunger and malnutrition. He also found short lifespans that he attributed to chronic malnourishment which left people susceptible to disease. Lifespans, height and weight began to steadily increase in the UK and France after 1750. Fogel's findings are consistent with estimates of available food supply.
Theories for the breakout
Causes for the Malthusian Trap and theories for the causes of the Industrial Revolution have been as multifarious as the theories of the fall of the Western Roman Empire. The transition from the Malthusian epoch to an era of sustained economic growth is explored by Unified growth theory. One branch of Unified growth theory is devoted to the interaction between human evolution and economic development. Some argue that natural selection during the Malthusian epoch selected beneficial traits to the growth process and brought about the Industrial Revolution. Consistent with the theory, evidence shows the survival of the richest in England during the 17th century.
From a macroeconomic perspective, the main contributions to the British breakout were technological improvements and structural change away from agricultural production, while coal, capital, and trade played a minor role.
Economic historian Gregory Clark has controversially argued, in his book A Farewell to Alms, that the British breakout may have been caused by differences in reproduction rates among the rich and the poor (the rich were more likely to marry, tended to have more children, and, in a society where disease was rampant and childhood mortality at times approached 50%, upper-class children were more likely to survive to adulthood than poor children.) This in turn led to sustained "downward mobility": the descendants of the rich becoming more populous in British society and spreading middle-class values such as hard work and literacy.
A trap at the escape from the Malthusian Trap
In 2011 it was suggested that the emergence of major sociopolitical upheavals at the escape from the Malthusian trap is not an abnormal, but a regular phenomenon.